Monday, February 22, 2010

So what did Darwin get wrong?

I have written a review for the Sunday Times of Jerry Fodor and Massimo Piattelli-Palmarini’s new book What Darwin Got Wrong. There was an awful lot to talk about here, and it was a devil of a job fitting it into the space available and getting it down to the appropriate level. Here’s how the review started (more or less). There’s considerably more to be said, but I’ve got too much else on the go at the moment. Suffice to say, the book is well worth a read, though it is not always easy going.
What Darwin Got Wrong
Jerry Fodor and Massimo Piattelli-Palmarini
Profile, 2010
ISBN 978 1 84668 219 3
Hardback, 262 pages
£20.00

Around 1.6 million years ago, our hairy ancestors began roaming further afield in search of food, and all that trekking got them hot and bothered. So they shed most of their hair evolved into us, the naked ape.

Thus runs one of countless stories of how evolution is driven by genetic adaptation to the environment: the conventional narrative of Neodarwinism. But according to cognitive scientists Jerry Fodor and Massimo Piattelli-Palmarini, they are all mistaken.

Despite their book’s unobjectionable title – of course there were things Darwin, who knew nothing of genes and DNA, got wrong – Fodor and Piattelli-Palmarini don’t simply think he missed a few details. Although they agree, indeed insist, that all of today’s flora and fauna evolved from earlier species, they don’t think that Darwin’s natural selection from a pool of random mutations explains it.

The arguments warrant serious consideration, but let’s first be clear about one thing. An honest reading of this book offers not a shred of comfort to creationists, intelligent designers and other anti-evolutionary fantasists. That, as the authors must know, won’t prevent the book being misappropriated, nor will it save them from the opprobrium of their peers (Fodor has already had a spat with arch-Darwinist Daniel Dennett).

In Neodarwinian theory, genes mutate at random across generations, and those that bestow an advantageous physiological or behavioural trait (phenotype) spread through a population because they boost reproductive success. But there’s often no simple connection between genes and phenotype. A single gene may have several roles, for example, and genes tend to work in networks so tightly knit that evolution can’t necessarily tinker with them independently of one another.

Naïve accounts of natural selection tend to award it quasi-mystical omnipotence, whereby it can effect just about any change, and every change is interpreted as an adaptation. The Scottish zoologist D’Arcy Thompson rubbished this habit almost a century ago, but it hasn’t gone away. The palette of biology is surely constrained by other factors: perhaps, say, the reason we don’t have three arms or eyes is not that they are non-adaptive but that they are not within the repertoire of fundamental body-forming gene networks.

Fodor and Piattelli-Palmarini also point out how ‘evidence’ for Darwinism is often conflated with evidence for evolution: ‘just look at the fossil record’. And post hoc adaptationist accounts of evolutionary change (such as the one I began with) risk being merely that: plausible but unscientific Just So stories. To the authors, that’s all they can ever be, because Darwinism is a tautology: organisms are ‘adapted’ to their environment because that’s where they live. How well adapted birds are to the air, and fish to the sea!

All of this is good stuff, and convincingly calls time on simplistic Neodarwinism. But as Fodor and Piattelli-Palmarini admit, many biologists today will say ‘Oh, I’m not that kind of Darwinist’: they know (even if they rarely say it publicly) that evolution is much more complicated. They agree that there is more to life than Darwin.

But Fodor and Piattelli-Palmarini seem to want to banish him entirely, claiming that natural selection is logically flawed because it can’t possibly identify what exactly is selected for. Their argument is opaque, however. Are frogs selected to eat flies, or to eat buzzing black things which just happen invariably to be flies? The authors don’t explain why the simple answer – find out in an experiment with frogs and faux-flies – won’t do. Their objection seems to be that evolution can’t do the experiment, because it is non-intentional and can’t know what it is looking for (they say Darwin’s reliance on stock- and pigeon-breeding therefore involved a false analogy for evolution). And they worry that we can’t distinguish adaptations from genetic changes that ‘free-ride’ on them.

But blind natural selection does work in principle, as computer models unambiguously show. These models are highly, perhaps excessively simplified. But if the same thing doesn’t happen as a rule in real populations, vague logical arguments won’t tell us why not. And if we struggle to work out precisely what trait has ‘adapted’, surely that’s our problem, not nature’s.

In any event, the authors admit that at least some of the many ‘textbook paradigms of adaptationist explanation’ might be perfectly correct. Some certainly are: superbugs have acquired antibiotic-busting genes, which is about as direct an adaptation as you can get. The authors don’t wholly exclude natural selection, then, but say it may simply fine-tune other mechanisms of evolutionary change (whatever they are). Specific adaptations, they say, are historical contingencies, not examples of a general law. In the same way, there may be good specific explanations for why your bus was late this morning, and also last Thursday, but they don’t in themselves to amount to a natural law that buses are late. Fair enough, but then to say whether adaptation is the exception or the default we need statistics. The authors are silent on this.

So they don’t quite achieve a coherent story, neither are they able (or perhaps willing) to convey it at a non-specialist level. Even so, they make a persuasive case that the role of natural selection in evolution is ripe for reassessment. To say so should not be seen as scientific heresy or capitulation to the forces of unreason – it’s a brave and welcome challenge.